Saccharide-branched Cyclodextrins as Targeting Drug Carriers

A synthetic series of heptakis-galactose-branched cyclodextrins (termed CDs) having a longer spacer arm using two amino-caproic acids as an enlarging unit were prepared. Starting with heptakis-amino-β-CD or heptakis-amino-caproic-amide-β-CD, treated with galactosyl-glucono-amide-caproic acid, the new compounds heptakis (Gal-cap1)-CD (4) or heptakis (Gal-cap2)-CD (5) were obtained. The longer galactose spacer arm extremely favors the PNA association. The effect of branch length on K with PNA was enhanced up to 138-fold 3 as well as with DXR enhanced up to 81-fold. Hexakis (Gal-cap2)-CD (6) was prepared and the association constants with rat liver cells were observed to be 2.5 × 10¹⁰ M⁻¹. A multi-high mannose type oligosaccharide branched CD (7) showed a large association constant with DXR up to 1.1 × 10⁹ M⁻¹. The two-dimensional map for the association constants of newly synthesized oligosaccharide-branched CDs toward lectin or liver cells versus the association constants toward a drug (doxorubicin) suggested a method of finding a better targeting drug carrier. The structural effect of the oligosaccharide-CDs showed that the number and length of the branch were dominant factors in designing for enhanced dual recognition.     

Development of a 6-hydroxychroman-based derivatization reagent: application to the analysis of 5-hydroxytryptamine and catecholamines by using high-performance liquid chromatography with electrochemical detection

We developed a novel derivatization reagent, (2R)-2,5-dioxopyrrolidin-1-yl-2,5,7,8-tetramethyl-6-(tetrahydro-2H-pyran-2-yloxy)chroman-2-carboxylate (NPCA), for electrochemical (EC) detection in HPLC. NPCA was synthesized from (R)-(+)-6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (alpha-CA), which exhibits intense EC response. NPCA successfully yielded alpha-CA derivatives of primary amines by a two-step derivatization procedure. Following pre-column derivatization with NPCA, a simultaneous determination of alpha-CA derivatives of neuroactive monoamines [dopamine (DA), epinephrine, and 5-hydroxytryptamine (5-HT)], their monoamine oxidase metabolites (3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindole-3-acetic acid) and their catechol-O-methyltransferase metabolites [3-methoxytyramine (3-MT) and normetanephrine (NMN)] was completely achieved using our HPLC-EC method. Using an HPLC equipped with coulometric electrode-array detection system, the resultant alpha-CA derivatives of NMN, 5-HT, DA and 3-MT showed intense EC responses, that were approximately 1.3, 1.4, 1.1 and 1.4-fold higher than the corresponding native forms, respectively. The detection limits were in the range of approximately 16-60 fmol on column (signal-to-noise ratio 3). The proposed HPLC method was applied to determine 5-HIAA, HVA, alpha-CA-5-HT and alpha-CA-DA in rat urine. As a consequence, these analytes were successfully determined with satisfactory precisions.     

Synthesis of selenylfullerene with selenium-containing dibenzo[b,g]cyclooctane moiety

The photochemical reaction of C₆₀ with selenium-containing bicyclooctanes affords for the first time the selenylfullerenes. The derivatives were characterized by mass, UV-vis absorption, NMR spectroscopy, and X-ray crystallographic analysis.     

Large-scale separation of metallic and semiconducting single-walled carbon nanotubes

In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way.     

Experimental investigation of amplitude death in delay-coupled double-scroll circuits with randomly time-varying network topology

Nonlinear Dynamics - The present study experimentally investigates amplitude death in delay-coupled double-scroll circuits with a time-varying network topology that randomly changes at a regular...     

Remarkable CO-catalyst effect of gold nanoclusters on olefin oxidation catalyzed by a manganese-porphyrin complex

The effect of dodecanethiolate-protected metallic nanoclusters of gold (Au:SC12, 1), silver (Ag:SC12), palladium (Pd:SC12), and platinum (Pt:SC12) on the catalytic activity of Mn(TPP)Cl (TPP = tetraphenylporphinato) was investigated in styrene oxidation with iodosylbenzene. Among the four metal clusters, only Au:SC12 led to appreciable acceleration of the catalytic reaction. The major role of the Au cluster was to regenerate the active catalytic path involving Mn(III) and Mn(V) from the deactivated Mn(IV) species. The binary 1/Mn(TPP)Cl catalyst system showed an absorption spectrum characteristic of Mn(III)-porphyrin after reaction, whereas a catalytically ineffective Mn(IV) species was observed as the sole porphyrin species in the absence of the Au cluster or in the presence of Pd, Ag, and Pt clusters. Accordingly, the slow oxidation reaction with Mn(TPP)Cl was accelerated by the addition of Au:SC12, and complete conversion of Mn(IV) into Mn(III) was observed in the absorption spectrum. 1H NMR inspection of the reaction of Au:SC12 and iodosylbenzene revealed that the surface dodecyl groups were partially oxidized into dodecanal and eliminated from the cluster surface, thereby producing unprotected gold sites on the surface. A reactivation mechanism involving the reaction of the Mn-porphyrin and the oxidant activated on the gold surface is proposed.